Revision as of 08:34, 23 January 2017

DNSCrypt encrypts and authenticates DNS traffic between user and DNS resolver. While IP traffic itself is unchanged, it prevents local spoofing of DNS queries, ensuring DNS responses are sent by the server of choice. [1]

Installation

Configuration

To configure dnscrypt-proxy, perform the following steps.

Select resolver

Select a resolver from /usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv and editdnscrypt-proxy.service, using the first column as the name of the resolver with the -R flag. For example, to select dnscrypt.eu-nl as the resolver, the drop-in file would look like this:

Change port

It is recommended to run DNSCrypt as a forwarder for a local DNS cache, otherwise every single query will make a round-trip to the upstream resolver. Any local DNS caching program should work. In addition to setting up dnscrypt-proxy, you must setup your local DNS cache program. See #Example local DNS cache configurations for more information.

In order to forward to a local DNS cache, dnscrypt-proxy should listen on a port different from the default 53, since the DNS cache itself needs to listen on 53 and query dnscrypt-proxy on a different port. Port number 5353 is used as an example in this section. In this example, the port number is larger than 1024 so dnscrypt-proxy is not required to be run by root. Editdnscrypt-proxy.socket with the following contents:

Tip: If you are setting up a server, add interface: 0.0.0.0@53 and access-control: your-network/subnet-mask allow inside the server: section so that the other computers can connect to the server. A client must be configured with nameserver address-of-your-server in /etc/resolv.conf.

The default size being 1252 bytes, with values up to 4096 bytes being purportedly safe. A value below or equal to 512 bytes will disable this mechanism, unless a client sends a packet with an OPT section providing a payload size.

Redundant DNSCrypt providers

To use several different dnscrypt providers, you may simply copy the original modified dnscrypt-proxy.service and dnscrypt-proxy.socket from #Configuration. Then in your new copy of the service change the provider. From there change the port in the new socket. Lastly, update your local DNS cache program to point to new service's port. For example, with unbound the configuration file would look like if using ports 5353 for the original socket and 5354 for the new socket.

This specifies an instanced systemd service that starts a dnscrypt-proxy using the service name specified after the @ symbol of a corresponding .socket file.

Add first dnscrypt-socket

Now create two or more socket files, specifying different DNSCrypt providers.

For the first dnscrypt-proxy socket, listening on 127.0.0.1@5353 and connecting to the example dnscrypt.eu-nl provider, copy /lib/systemd/system/dnscrypt-proxy.socket to /etc/systemd/system/dnscrypt-proxy@dnscrypt.eu-nl.socket and edit the file to reflect the correct port (5353 in this case).

Add additional dnscrypt-sockets

Here you can replace the socket instance name to eg. cloudns-syd as one of those listed in providers name column in /usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv and edit it to port 5354 and so forth.

[Unit]
Description=dnscrypt-proxy-secondary listening socket

[Socket]
ListenStream=127.0.0.1:5354
ListenDatagram=127.0.0.1:5354

[Install]
WantedBy=sockets.target

Apply new systemd configuration

Now we need to reload the systemd configuration.

# systemctl daemon-reload

Since we are replacing the default service with a different name, we need to explicitly stop and disablednscrypt-proxy.service and dnscrypt-proxy.socket.

Now start/enable the new service(s), e.g., dnscrypt-proxy@dnscrypt.eu-nl, etc.